The present invention resides in the field of fire suppression, and more particularly fire suppression for flammable liquid storage tanks. The invention is intended for use in land or vehicle housed storage tanks for retaining volatile, flammable fluids that has a gap between the storage tank shell or outer wall and a floating roof for covering the stored fluid.
Bulk fluids, such as petroleum, other fuel products and by-products, and chemicals are often stored in large tanks. These tanks are commonly designed with internal floating roofs or bulk fluid covers to minimize product losses to the outside environment and contain volatile gases within the confines of the storage tank. A critical part of the internal floating roof is the annular or rim space between the perimeter of the internal floating roof and the inner wall of the storage tank. In order to retain separation between the stored volatile fluid and the outside environment a rim space seal must be employed.
Three types of rim space seals are commonly known in the industry. These types of seals have been tested for their efficiency in reducing evaporative losses from the rim space. The seal types are: liquid-mounted resilient-filled seal; mechanical shoe seal; and vapor-mounted resilient-filled seal. These seals have been used for decades and their relative length of service is known. Testing has revealed that the most efficient seal is a liquid-mounted seal, followed by a mechanical shoe seal and finally a vapor-mounted seal. Seal efficiency has been shown to increase when a secondary seal is placed above the first seal.
The rim space in a storage tank is prone to fires due to lightning strikes or other spontaneous combustion due to static electricity, accumulated over-heated gas, and the like. The energy surge will ignite the product stored in the tank in any exposed area such as the rim space. Considerable effort has been put into the design of tanks to install fire extinguishing systems that fight rim space fires.
Conventional firefighting systems usually consist of a foam delivery apparatus that is commonly manually activated by personnel monitoring the storage tank. The fire extinguishing system would be activated upon detection of a fire within the storage tank. Detection can occur when an internal sensor indicates an alarm condition or by external visual indication such as smoke. Either occurrence may span a considerable amount of time in order to detect a fire, allowing the fire to expand to the entirety of the storage tank rim space. In addition, the heat of the expanded fire may affect the structural integrity of the storage tank wall. A significantly reduced fire would significantly reduce the high temperatures of a rim space fire and minimize potential damage to the storage tank wall; also preventing a more catastrophic event of a breach or explosion.
Storage tanks housing flammable fluids are usually outfitted with a rim space foam delivery firefighting system. The foam will inundate the rim space to suppress and eventually remove the oxygen from the surface of the fluid extinguishing the fire. In practice, the time period from the time a fire is detected until the foam is actually delivered to the rim space at the fire location is approximately 3-5 minutes after activation. However, it can take up to several hours or even days for visual smoke to be seen emanating from the rim space of a tank to be noticed or for the fire detection systems to indicate a positive detection of a fire. Only then will the foam system be activated. In such an extended time period, a fire could expand from a localized area to one that could encompass the entire rim space.
One fire protection device that appears to have a similar construction is described in U.S. Pat. No. 6,948,567 [Cyphers, et al.] teaches the use of a rectangular box-like container for holding a fire extinguishing material that will disperse that material under either a ballistic or explosive impact or through heat induced melting of the outer face. The fire extinguishing material is described as a powder and the container is structured with internal ribs for transferring energy from the rear side to the front in order to shatter or create a fissure for the fire extinguishing material to disperse. However, there is no direct indication at what location this box-like container would be placed in a storage tank holding flammable liquids.
It is, therefore, an object of the present invention to provide a fire suppressant system that is located within the rim space of a storage tank in substantial proximity to the fluid surface. It is a further object of the present invention to maintain that close proximity of the fire suppressant system to the fluid surface by allowing the fire suppressant system to rise and fall with the fluid level within the storage tank.
It is also an object of the present invention to provide the fire suppressant material and container in such location as to not interfere with the sealing system between the floating roof and the storage tank wall, or conversely, the sealing system to not interfere with the fire suppressant system. It is yet another object of the present invention to provide a fire suppressant system composed of intumescent materials in the form of smaller bodies housed within a box-like container that will release the bodies in response to intense heat or ballistic or explosive contact spreading the intumescent bodies across the surface of the flammable liquid.
Other objects will appear hereinafter.